Fluorine-containing rubbers exhibit excellent chemical resistance, solvent resistance and heat resistance, and therefore, are widely used in various fields such as automobile industry, semiconductor industry and chemical industry. For example, in automobile industry, fluorine-containing rubbers are used as hoses, sealing materials, etc. for engine and its peripheral equipment, driving equipment, and fuel system and its peripheral equipment.
However, fluorine-containing rubbers, for example, propylene/tetrafluoroethylene copolymer rubber, etc. are subject to embrittlement at low temperatures in some cases, and for improvement therefor, there is proposed a method of blending an ethylene/tetrafluoroethylene copolymer resin (ETFE) having a melting point of 240° C. to 300° C., and after melt-kneading, carrying out radiation crosslinking or peroxide crosslinking (Patent Document 1).
Also, in Patent Document 2, there is described a method of press-crosslinking a fluorine-containing rubber composition comprising a fluorine-containing rubber (vinylidene fluoride (VdF) type rubber), a fluorine-containing resin (ETFE) and a fluorine-containing thermoplastic elastomer (at 160° C. for ten minutes) and then crosslinking in an oven (at 180° C. for four hours) to produce a crosslinked rubber having improved thermal strength.
These Patent Documents do not mention surface characteristics, particularly characteristics of a crosslinked rubber. This is because rubbers are inherently high in friction coefficient due to elastomeric property thereof.
Accordingly, in the field of sealing materials, a method of laminating a fluorine-containing resin (or a fluorine-containing resin fiber layer) on a surface of rubber (Patent Documents 3 and 4) and a method of forming a coating film of a fluorine-containing resin on a surface of rubber (Patent Document 5) as a method of decreasing friction coefficient while making best use of rubber characteristics.